This invention is directed to a molding composition comprising a blend of select poly(aryl ketone)s and a polyetherimide.
Poly(aryl ketone)s are a known class of engineering polymers. Several poly(aryl ketone)s are highly crystalline with melting points above 300.degree. C. Two of these crystalline poly(aryl ketones) are commercially available and are of the following structure: ##STR1##
These poly(aryl ketone)s exhibit a superior combination of properties, i.e., superior thermal and hydrolytic stability, high strength and toughness, superior wear and abrasion resistance and superior solvent resistance. Thus articles molded from poly(aryl ketone)s have utility where high performance is required.
Polyetherimides are also commercially available. They are amorphous thermoplastic polymers with high heat resistance, high strength and modulus, and high dielectric strength. Polyetherimides can be molded into a variety of articles. However, the ultimate use temperature and solvent resistance of the polyetherimides is not acceptable in end use applications where such properties are required. Thus, there is a need to improve these properties without essentially affecting other properties.
In the present invention it has been found that blends of select poly(aryl ketone)s and polyetherimides are very compatible, in fact, they tend to form one phase in the amorphous state, and thus are miscible systems. As a result, such blends can significantly improve the ultimate use temperature and stress crack resistance of the polyetherimide.
Due to the miscibility of these blends, injection molded samples of the blends are transparent even though the poly(aryl ketone) is opaque under normal injection molding conditions. Further, with proper annealing, opacity due to crystallization of the poly(aryl ketone) can be accomplished.
Further, the blends of poly(etherimides) and poly(aryl ketones) may used in a number of diverse high performance applications. These applications include electrical/electronic applications where the addition of a poly(aryl ketone) to a polyetherimide improves the solvent resistance so that solvent cleaning (e.g., trichloroethylene degreasing) can be utilized without part failure due to environmental stress cracking. Polyetherimide modification of the poly(aryl ketone) may be used in composites containing carbon fiber where improved stiffness at 300.degree. F. is required. This is a specific temperature requirement for certain composite applications, and the increased glass transition temperature (Tg) of the poly(aryl ketone) with the polyetherimide improves this deficiency for poly(aryl ketone)s having low Tg's.
The addition of polyetherimide to poly(aryl ketone) should improve the permeability to such gases as H.sub.2, CO.sub.2, O.sub.2, N.sub.2, etc.; this coupled with the enhanced solvent resistance of the blends compared to that of polyetherimide makes the blends of this invention useful in membranes for the separation of gases, reverse osmosis and ultrafiltration. Conversely, the addition of a poly(aryl ketone) to a polyetherimide would result in a decrease in the permeability to certain gases and thus these blends are useful in the fabrication of barrier films for use in, for example, packaging.
Further, the addition of a poly(aryl ketone) to a polyetherimide results in an enhancement in toughness. These blends exhibit toughness exceeding that of either constituent.
In the case where an amorphous polyetherimide is blended with a crystalling poly(aryl ketone), the resultant blend has reduced mold shrinkage and increased dimensional stability than the poly(aryl ketone).